A magnetic head and disk tester is an instrument that is used for testing the characteristics of magnetic heads and disks such as a signal-to-noise ratio, track profile, etc. The tester should simulate those motions of the head with respect to the disk and the same rotational speeds of the disks that occur in an actual hard disk drive during operation. Each tester consists of two components, i.e., a mechanical component, commonly referred to as a spinstand, that performs movements of the head with respect to the disk, and an electronic component that is responsible for measurement, calculation, and analysis of the measured signal. The spinstand is also a mechanical component of a servo-writer, an instrument that is used for writing servo information on a magnetic disk, as well as a component of a flying height tester; an instrument used for measuring the flying height of a head over the disk.
A typical prior art spinstand for a head and disk tester is illustrated in FIG. 1 (front view) and FIG. 2 (top view). The spinstand includes a stationary base plate 10 that supports walls 12a, 12b, 12c. The walls 12a, 12b, 12c in turn support a spindle 13 for carrying a disk pack DP disposed in a cylindrical disk pack region including one or more magnetic disks 14 having diameter D and having arranged in parallel, and b being coaxial about a disk pack axis DPA. The spindle 13 and disks 14 are rotated by a spindle motor 15 about a spin axis.
The base plate 10 further supports first and second slide motors (not shown). The first slide motor moves a slide 16 along rails 17a, 17b in the Y direction (see FIG. 2). Two additional rails, 18a, 18b, are mounted on top of slide 16. The second slide motor controls movement of a second slide 19 along rails 18a, 18b in the X direction. The first and second motors cooperate to position a rotary positioner 20 mounted on slide 19 to a specified location with respect to the center of spindle 13. Rotary positioner 20 carries and positions magnetic head(s) 22 relative to disk(s) 14.
As the density of magnetic recording increases, additional information tracks are compressed into a given disk area. The decrease in track size heightens the demand for improved accuracy in head positioning. Likewise, the rotational speeds of the magnetic disks increase in order to achieve shorter access times. In addition, more disks are added to the disk stack to provide additional storage.
As the disk(s) rotate they cause the air around them to circulate, which creates a region of low pressure surrounding the disk(s). Due to this low pressure, air is drawn in from the top and bottom surfaces of the disk(s) and is moved outward from the spindle center. The air flow generates vortexes that induce vibrations in both the disks and the magnetic heads. These vibrations increase track misregistration. As the rotational speeds increase, vortexes generated by the rotating disk(s) increase significantly, and the vibrations and track misregistration reach unacceptable levels. Track misregistration is further exacerbated due to the change of the ambient temperature, which results in the expansion, or contraction of the magnetic disk. Furthermore, with more disks in the stack, the stack has a higher propensity to vibrate, causing further track misregistration. In some cases, track misregistration reaches unacceptable levels at which spinstand operation becomes unreliable.
Electromagnetic shielding is a further important consideration because electromagnetic radiation in the air tends to increase the noise level and degrade the quality of the signal read from the magnetic disk.
In spinstands, there is a danger of the magnetic disk(s) breaking or becoming detached from the spindle, due to mechanical defects in the material of the disk(s) and/or a failure of the clamping mechanism that is used to hold the magnetic disk(s) on the spindle. With increasing rotational speeds of the magnetic disks, this danger and the risk of injury to the operator of the spinstand increases.
Spinstands are usually operated in clean room environments as it is necessary to protect the magnetic disks and the heads from contamination. The contamination can occur due to dust particles in the air, or by accidental contact of the operator with the heads and disks.